One of the only remaining structures from the original castle, the Hyakunin-bansho which, appropriately enough, was named because it could house over 100 samurai. It was the largest of the guardhouses along the main road to the honmaru, and served as the major checkpoint before coming to the chujaku-mon, the final gate on the approach.
Edo-jo was largest castle ever built in Japan with a massive complex and towering, 58 meter tenshu. It was built by Ota Dokan in 1457, and later became the center of Tokugawa Ieyasu's bakufu. Prior to 1590, it was under control of the Hojo. However, they were defeated when Odawara was taken (and along with it, Edo-jo) by Hideyoshi and later transferred to Ieyasu. The grounds is somewhat restricted as it is has been the imperial residence, Kokyo, since the Meiji era. However, you can tour the grounds and garden and see the site of the original tenshu (donjon).
Edo Castle (Kokyo). Chiyoda, Tokyo.